on Meson-Nucleon Physics and the Structure of the Nucleon

We reanalyze data from ELSA on ω production in nuclei, from where claims of a large shift of the mass were made earlier, which are tied to a certain election of the background in nuclei, very different in shape to the one on the proton. The reanalysis shows that the data demand a very large width of the ω in the medium, with no need for a shift of the mass, for which the experiment is quite insensitive. We study possible ω bound states in the nucleus and find that, even assuming a small width, they could not be observed with the present ELSA resolution. Finally we show that, due to the interplay of background and ω signal, a two bump structure appears with the ELSA set up for the (γ, p) reaction that should not be misidentified with a signal of a possible ω bound state in the nucleus.